Pinterest's Growth Comes Back to Earth

Pinterest hit ten million monthly unique visitors faster than any other website, drawing comparisons to Facebook. But now growth of the service for sharing images from across the web in "virtual scrapbooks" is coming back to earth.

Data through March 18th which Comscore shared exclusively with CNBC reveal that the company's growth has started to slow this month.

The technical details: a four week moving average of Pinterest's unique users showed that growth slowed from an 85% rate between mid-January and mid-February, to an 18% rate between mid February and mid-March. Based on the latest data Comscore projects that Pinterest will grow its total unique users in March to just over 20 million, just a roughly 12 percent month-over month increase, after posting a 50 percent increase in February.

Yes, the company continues to grow by double digits, but the rate of growth is coming back to earth. ComScore's VP of Industry Analysis drew the comparison to Twitter, pointing out that after Twitter catapulted from 4 million to 20 million uniques over just a three month period, it was stuck at 20 million for quite some time, because those new users habits hadn't solidified yet.

And now the startup is scrambling to address legal issues. Up until last week Pinterest encouraged users to "avoid self promotion," which meant gathering photos from across the web to share, rather than sharing their own photos. But many of the photos people share from the web are copyrighted, which open users up to lawsuits. Pinterest itself is protected by the Digital Millennium Copyright Act, which requires websites pull offending content when alerted. But if users start seeing lawsuits, they won't want to spend time on the site.

So on Friday Pinterest introduced new policies, telling users to only "pin" content they create or have permission to use. Limiting the scope of images users share could make the service less compelling. But lawsuits-- we haven't seen any yet-- would be a bigger problem.

Even if Pinterest is on track to plateau for a while - it's still a unique way to allow people to share images. Copyright issues haven't stopped President Obama from taking to the platform to reach a certain demographic: Pinterest users skew female, midwestern and suburban. On Tuesday the Obama campaign launched eight pinterest boards, including Obama-inspired recipes, merchandise, art, as well as the serious stuff-- information on his policies.

CNBC has also jumped on the Pinterest bandwagon-- http://pinterest.com/cnbcpins/ CNBC pins photos and quotes from interviews -- check it out!